This invention relates to the production of an expanded food product. More particularly, the invention relates to a method and apparatus for incorporating an additive uniformly throughout an extrusion-expanded food product.
The production of extrusion-expanded food products, both those intended for human consumption and those for use as pet foods, is well known in the food industry. Typically such products are produced in an extrusion cooker of the general type disclosed in U.S. Pat. Nos. 3,117,006 and 3,385,709, in which a moistened mixture of farinaceous and/or proteinaceous materials is introduced into the extruder in which the mixture is subject to mechanical working at elevated temperatures and pressures and is extruded through an extrusion die into the atmosphere. As the material issues from the die, it expands into a porous expanded product due to the pressure drop across the die and the flashing off of water as steam. The extrudate is then cut into pieces of a desired length and dried. Examples of food products for human consumption which can be prepared by such procedures are disclosed in U.S. Pat. Nos. 3,104,975 to Bowman, 3,117,006 to Wenger and 3,385,709 to Wenger et al, and examples of the production of expanded animal food products are disclosed in U.S. Pat. Nos. 3,119,691 to Ludington et al, 3,447,929 to Hale, and 3,891,774 to Baker et al.
While the expanded food products produced by such procedures are nutritious, it is frequently desired to incorporate one or more additives such as flavoring materials, palatability enhancers, coloring agents, and the like in the expanded product to improve the flavor of the product, or provide the expanded product with the appearance of meat, and the like. Melted fat, usually tallow, is commonly coated onto the product to improve its palatability, particularly when pet food products are being produced. For example, U.S. Pat. No. 3,119,691 to Ludington et al discloses coating the expanded particles with fat and a liquid meat extract. U.S. Pat. No. 4,104,407 to Stringer et al discloses coating the expanded particles with a dextrin material and fat. U.S. Pat. No. 4,215,149 to Majlinger discloses coating the expanded particles with fat and a salt of phosphoric acid. U.S. Pat. No. 3,745,023 discloses coating the expanded particles with a composition containing modified animal fat extracts, vegetable oil and fish oil. U.S. Pat. No. 4,211,797 to Cante et al discloses coating expanded particles with a blend of lipolyzed beef tallow and digest of beef. In each of these disclosures, the fat and other additives are incorporated by coating the material on the surface of the expanded pieces, such as by spraying, tumbling, dipping, and the like. While such an application of the additive is effective to enhance the palatability or other characteristics of the expanded food, it is subject to certain disadvantages. For example, an additional processing step is required in the production of the product. Moreover, when fat is applied to the surface of the expanded pieces, the fat-coated surface is greasy and requires packagers to sell the product in grease-resistant lined containers, since paper containers absorb the fat, resulting in an unsightly package. Also, the fat coating on the product is exposed to the oxygen of the air and is thus subject to oxidative rancidity.
Prior attempts to include such additives, particularly fat, directly into the matrix of the expanded product have not been entirely successful. Thus, when fat is added to the farinaceous and/or proteinaceous mix in the expander, the fat has a tendency to be expressed from the ingredient mix during the extrusion process. Attempts to add substantial amounts of fat directly to the ingredient mixture prior to extrusion have reduced product expansion to such an extent that the products become undesirably dense. In order to avert these difficulties, a number of procedures have been suggested heretofore in order to incorporate fat or other additives in the matrix of the expanded product by the addition of fat and other additive to the ingredient mixture prior to extrusion, such as disclosed in U.S. Pat. Nos. 3,908,025 to Miller et al, 4,020,187 to McCulloch et al, and 4,225,630 to Pitchon.